At last there are signs of a change of climate over climate change. Seven years of alarmism have yielded endless conferences and gargantuan sums of public expenditure, with no serious impact on carbon emissions. In a bitter irony, the state that has been most hostile to the concept, America, has been the leader in emissions reduction, largely through a free market shift from coal to gas.

Today's report by the Intergovernmental Panel on Climate Change should silence those who believe there is no debate to be had. On even the mildest precautionary principle, policymakers should take note of the shifts – whether temporary or lasting – in the composition of the earth's atmosphere. They are told to look with their own eyes at specific impacts, from glaciation to crop and fish yields. Sceptics may challenge some of these, but the balance of probability is clear. Something is happening that will matter to most of the world's inhabitants.

At this point, many of the old obstacles arise. Powerful, debate-distorting lobbies have developed behind the huge sums of money at stake on either side. Where this report is helpful is in pluralising that debate away from mere alarmism – wasted on costly and often futile spending on "renewables" – towards thinking intelligently about how the world should adapt to what is already happening. If Rome is burning, there is no point in endlessly retuning Nero's fiddle. As Chris Field, one of the authors, points out, science now offers "a clearer understanding of what we can and cannot achieve through mitigation and adaptation together".

Needless to say that does not wholly avert controversy. The author of the economic chapter, Britain's Richard Tol, asked for his name to be removed as the final draft proved more alarmist than what he had seen, especially in downplaying adaptation. Just as change harms some crops, he says, it aids others. "Farmers adapt. They are not stupid," he says. "It is pretty damn obvious that there are positive impacts of climate change, even though we are not always allowed to talk about them."

Clearly the old dogmatism still curses this debate, but it does seem that the dam of orthodoxy is cracking. No interest group or lobby, no argument or scepticism, can be off the agenda. Climate change must invade territory that has proved anathema to many of its more virulent champions. This may have to involve defence and aid expenditure, nuclear power, GM foods, gas fracking, water management, migration, energy and farm subsidies. If climate change is as critical as the scientists claim, there can be no sacred cows. Nothing can be off limits.